1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic apparatus, an electrostatic recording apparatus, etc.
2. Related Background Art
The general operations of an image forming apparatus such as an electrophotographic apparatus, an electrostatic recording apparatus, etc. are described below by referring to FIG. 22.
FIG. 22 shows an entire configuration of an example of a typical image forming apparatus, that is, an image forming apparatus for forming an image on a transferring material using an electrophotographic process.
An electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1, which is a drum-shaped image bearer, and is rotation-driven at a predetermined process speed in the direction of an arrow R9 shown in FIG. 22, and an image forming process such as a charging process, an image exposing process, a developing process, a transferring process, a cleaning process, etc. is performed on the photosensitive drum 1.
The above mentioned image forming process of forming an image to a transferring material is described as follows. First, the rotation-driven photosensitive drum 1 is charged such that its surface can have predetermined polarity and predetermined potential by a primary charging unit 2. In the following explanation, the photosensitive drum 1 is assumed to be charged to have negative polarity.
Then, the surface of the photosensitive drum 1 which is charged to have the negative polarity of predetermined potential is image-exposed by an exposing unit 3 (for example, a projection exposing unit for an original image, an image-modulated laser beam scanning exposing unit, etc.) as an image information write means, thereby attenuating the charging potential of the image-exposed portion (exposed light portion) and forming an electronic latent image corresponding to the exposed image information on the surface of the photosensitive drum 1.
The electronic latent image formed on the surface of the photosensitive drum 1 is sequentially made into a visible image as a transferable toner image by developing a toner image by a developing roller 4a of a developing unit 4 in a developing portion N6.
The system of exposing and developing the surface of the equally charged photosensitive drum 1 can be a normal developing system of exposing a background portion (in which no images are formed) of the image information on the surface of the charged photosensitive member, and developing the portion (in which an image is formed) other than the background portion, and a reversal developing system of exposing the portion of the image information, and developing the exposed portion.
Then, the toner image formed on the surface of the photosensitive drum 1 by a development portion N6 is transferred on the transferring portion N5 by the transferring means to the transferring material (transfer sheet) fed by a sheet feeding apparatus 13. The above mentioned transferring means can be, for example, a roller-shaped contact transfer charging unit (hereinafter referred to as a transferring roller 9). The transferring roller 9 is formed by, for example, a plug and an elastic layer enclosing the plug with the transferring portion N5 (transfer nip portion) formed by pressure-welding the layer to the photosensitive drum 1 with a predetermined pressure, thereby rotating the roller in the direction of the rotation of the photosensitive drum 1 (the R10 direction shown in FIG. 8) at a process speed almost equal to the process speed of the photosensitive drum 1 in the transferring portion N5.
Furthermore, the transferring material fed by the sheet feeding apparatus 13 is conveyed by a resist roller 15. The transferring material is conveyed to the transferring portion N5 such that when the tip portion of the toner image formed on the surface of the photosensitive drum 1 reaches the transferring portion N5, the tip portion of the transferring material can simultaneously reach the transferring portion N5.
The transferring material conveyed to the transferring portion N5 tightly contacts the photosensitive drum 1, held by the transferring portion N5 while the toner image is transferred from the photosensitive drum 1. In the period from the arrival of the tip portion of the transferring material at the transferring portion N5 to the passage of the rear portion of the transferring material through the transferring portion N5, a transferring bias (voltage) of predetermined positive polarity from a transferring bias (voltage) power supply not shown in the attached drawings is applied to the plug of the transferring roller 9.
In the process of the transferring material nipped and conveyed by the transferring portion N5, the toner image on the photosensitive drum side is sequentially transferred to the transferring material by the effect (of the transferring roller 9 of the positive polarity attracting the toner of the negative polarity) of the transfer field formed by the transferring roller 9 as a contact transfer charging unit and the pressure in the transferring portion N5.
Afterwards, when the rear end of the transferring material passes the transferring portion N5, the transferring material is separated from the surface of the photosensitive drum 1 and conveyed to a fixing unit 12, and the toner image transferred to the transferring material is fixed onto the surface of the transferring material as a permanently fixed image, and is then discharged as an image product (copy, print, etc.).
After the rear end of the transferring material passes the transferring portion N5, the accretion such as residual toner, powdered paper, etc. is removed (swept) from the surface of the photosensitive drum 1 by a cleaner 10. If images are continuously formed, a charging roller is repeatedly provided in forming an image. The residual toner, the powdered paper, etc. are stored in a waste toner container 11.
The present invention aims at providing an improved image forming apparatus. Furthermore, the present invention aims at providing an image forming apparatus including: an image bearer for bearing an image formed by a transferring material; a charging portion for charging an image bearer by predetermined potential; an exposing portion for forming an electronic latent image by exposing an image forming area of the image bearer charged by predetermined potential; a developing portion for developing an electronic latent image on the image bearer so that an image to be formed on the transferring material can be formed on the image bearer, wherein a voltage set in the developing portion for the image forming area of the image bearer is different from a voltage set in the developing portion for the non-image-forming area of the image bearer; a transferring portion for transferring an image formed on the image bearer to a transferring material; a transferring current detecting portion for detecting the transferring current flowing through the transferring portion; and a control portion for controlling the voltage set in the developing portion, wherein the voltage set on the developing portion of the image bearer is controlled based on the transferring current value detected by the transferring current detecting portion.
Another object of the present invention will become more apparent by reference to the following detailed description of the invention taken in conjunction with the accompanying drawings.